Gas turbine engines have a high temperature exhaust that requires suitable exhaust ducting in most installations. In particular, a gas turbine engine that serves as an auxiliary power unit (APU) in an aircraft generally mounts within a restricted space in a tail section of the aircraft. Such a gas turbine engine must operate within stringent noise limits when operating whilst the aircraft is on the ground. An exhaust ducting system for such a gas turbine engine preferably comprises a straight section of exhaust duct between the gas turbine engine or an exhaust silencer and an exhaust exit in a tail cone of the aircraft for such engine to minimise exhaust noise due to aerodynamic flow separation at the exhaust exit. Such installations have required mounting of the exhaust duct and exhaust exit along the centreline of the tail cone.
However, it is often desirable to duct the gas turbine exhaust to exit on one side of the aircraft tail cone to shield exhaust noise from critical locations. Such installations have a turn near the exit of the exhaust duct to accommodate the side-mounted exhaust exit. However, there is a noise penalty to such an arrangement because the turn in the exhaust duct upstream of the exhaust exit causes aerodynamic flow separation of the exhaust gases, thereby increasing exhaust gas velocity and flow noise. Even the inclusion of an exhaust silencer is no help in this case, since generation of this flow noise is downstream of the exhaust silencer.